The present invention relates to an image peaking method and the apparatus thereof, and more particularly to a vertical peaking method and the apparatus thereof, for peaking the vertical contour of an image according to its brightness.
Generally, in a digital television for processing a composite video signal, several vertical peaking methods have been suggested and accordingly, the vertical resolution of the image has been improved.
An example of the conventional techniques is the Korean patent application No. 89-4463 entitled "vertical peaking method of a screen in a digital television" and filed on Apr. 4, 1989 by this applicant. In the specification and the drawings of the Korean patent application No. 89-4463, the specific constitution and the description of the operation are detailed. Consequently, only a brief description will be given here. In the conventional vertical peaking method, as shown in FIG. 1, a vertical transition component, i.e., a signal difference between the upper and lower lines of the representative scanning lines a, b, and c, is detected as shown in FIG. 3A and the frequency spectrum destribution of the vertical transition component is shown in FIG. 2 and includes oblique lines. When the vertical transition, i.e., a contour component of the vertical direction, is detected as shown in FIG. 3A, the detected signal is secondarily differentiated, thereby detecting a difference component between lines as shown in FIG. 3B. The detected difference component between lines is added to the vertical transition component signal to peak the vertical contour component as shown in FIG. 3C, thereby improving the vertical resolution.
But, the disadvantage of the aforementioned vertical peaking method is that the effect is nonlinear with respect to the image brightness. The magnitude of the difference component between lines as shown in FIG. 3 varies according to the level of the luminance signal which determines image brightness. That is, if the level of the luminance signal is low, the magnitude of the difference component between lines is small, and if the level of the luminance signal is high, the magnitude of the difference component between lines becomes larger.
Thus, as the image becomes darker, the magnitude of the difference component between lines becomes smaller. Accordingly, the vertical peaking on a dark screen is less effective than on a bright screen.
On the other hand, the Japanese patent laid-open publication no. "Sho 63-121382" shows the method which can provide a high resolution luminance signal having no cross-color phenomenon. But, to remove the cross-color phenomenon, the image contour signal is further peaked, so that generating an unnatural appearance of a thick line in the image contour.